Control systems for valve actuators, valve actuators and related systems and methods

ABSTRACT

Valve systems and related methods include valve actuators and control systems configured to monitor at least one characteristic of the valve system during movement of a valve element to a position in the valve system and to determine a drift of the position based on the monitored at least one characteristic of the valve system.

RELATED SYSTEMS AND METHODS

This application is a continuation of U.S. patent application Ser. No.16/388,656, filed Apr. 18, 2019, for “CONTROL SYSTEMS FOR VALVEACTUATORS, VALVE ACTUATORS AND RELATED SYSTEMS AND METHODS,” thedisclosure of which is hereby incorporated herein in its entirety bythis reference.

TECHNICAL FIELD

The present disclosure relates generally to valve actuators, and moreparticularly, to control systems for valve actuators and related systemsand methods.

BACKGROUND

Valves include devices for both liquids and gases. Valve actuators areused to operate valves and are manufactured in numerous shapes, sizes,forms, and have a wide variety of utilities. Valve actuators may bemanually driven, electrically driven, operated by fluid pressure inwhich the shaft is connected directly or indirectly to a fluid operatedpiston, or other hydraulic systems. For example, the valve actuator maybe manually driven, operated by fluid pressure in which the shaft isconnected directly or indirectly to a fluid operated piston, or bedriven by an electric motor or through electro-hydraulic orelectro-fluid methods. Conventional valve actuators comprise anelectrically driven input shaft, which may be rotatable at relativelyhigh speeds with relatively low torque. The input shaft may, throughreducing gears such as a worm gear or a helical screw thread and nut,rotate a relatively high torque, low speed output shaft.

Actuators are often sized such that they can provide more torque thannecessary to fully seat a given valve. It may be desirable to determinethe torque generated by the output shaft or drive sleeve of a valveactuator. For example, when a valve is approaching a fully closed and/orfully seated position, the torque required to operate the valve may beconsiderably higher.

Actuators generally need to control or limit the amount of torque thatcan be applied to the load in a manner that is appropriate for variousoperating modes in a given application. If a torque threshold isexceeded, then a torque sensor may disengage or cease operation of themotor or otherwise cease the operation of the actuator. The torquethreshold may be fixed by the user at startup and may remain fixed untilphysically changed by the user. In such a situation, the valve actuatormay cease operation without completing movement of the valve, which mayresult with the valve not in a fully seated or closed position.

In addition to setting torque thresholds, the actuator may be configured(e.g., initially configured) to move a valve element to a selected fullyseated or closed position of the valve. However, the fully seated orclosed position of the valve may vary over time due to variation in theoperation conditions of the valve assembly, such as, material buildup onthe seating surface and/or the valve, wear on the seating surface and/orthe valve, or combinations thereof. The drift of the fully seated orclosed position of the valve effects the ability of the actuator toensure that the valve is correctly positioned in the fully seated orclosed position.

BRIEF SUMMARY

In some embodiments, the present disclosure includes a valve systemcomprising a valve actuator for controlling a position of a valveelement in a valve in order to control flow through at least a portionof the valve and a control system for controlling the valve actuator.The control system may be configured to: instruct the valve actuator tomove the valve element toward an unobstructed first position in thevalve to enable fluid flow through the at least a portion of the valve;instruct the valve actuator to move the valve element to a secondposition in the valve to reduce or increase fluid flow through the atleast a portion of the valve; monitor at least one characteristic of thevalve system during movement of the valve element to the secondposition; and determine a drift of the second position based on themonitored at least one characteristic of the valve system.

In additional embodiments, the present disclosure includes a valvesystem comprising a valve actuator for controlling a position of a valveelement in a valve in order to control flow through at least a portionof the valve and a control system for controlling the valve actuator.The control system may be configured to: instruct the valve actuator tomove the valve element to a target position from an initial position inthe valve to reduce or increase fluid flow through the at least aportion of the valve; monitor at least one characteristic of the valvesystem during movement of the valve element to the target position; anddetect a location of the target position based on the monitored at leastone characteristic of the valve system. The control system may befurther configured to at least one of: move the valve element intocontact with a seat of the valve system in the target position and thento force the valve element into the seat until a selected value oftorque in the valve actuator is reached; or substantially maintain alocation of the open position while actively adjusting the location ofthe target position based on the monitored at least one characteristicof the valve system each time the valve element is moved to the targetposition.

In yet additional embodiments, the present disclosure includes a methodof operating a control system of a valve actuator. The method includesmoving a valve element with the valve actuator to a closed position tosubstantially inhibit fluid flow through at least a portion of thevalve; monitoring at least one characteristic of the valve system duringmovement of the valve element to the closed position; determining adrift of the closed position based on the monitored at least onecharacteristic of the valve system; and at least one of: moving thevalve element with the valve actuator toward an open position lacking ahard stop in the valve to enable fluid flow through the at least aportion of the valve; moving the valve element into contact with a seatof the valve system in the closed position and then forcing the valveelement into the seat until a selected value of torque in the valveactuator is reached; or substantially maintaining a location of the openposition while actively adjusting the location of the closed positionbased on the monitored at least one characteristic of the valve systemeach time the valve element is moved to the closed position.

The features, advantages, and various aspects of the present disclosurewill be apparent to those skilled in the art from a consideration of thefollowing detailed description taken in combination with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the presentdisclosure, the advantages of this disclosure can be more readilyascertained from the following description of the disclosure when readin conjunction with the accompanying drawings.

FIG. 1 is a cut-away view of an electrically driven valve actuator.

FIG. 2 is cross-sectional view of a pneumatically driven valve actuator.

FIG. 3 is a chart illustrating a method of operating a control system ofa valve actuator in accordance with an embodiment of the presentdisclosure.

FIG. 4 shows an example graph indicating profiles of movement of thevalve in accordance with an embodiment of the present disclosure.

FIG. 5 is another chart illustrating a method of operating a controlsystem of a valve actuator in accordance with an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

As used herein, the term “substantially” or “about” in reference to agiven parameter means and includes to a degree that one skilled in theart would understand that the given parameter, property, or condition ismet with a small degree of variance, such as within acceptablemanufacturing tolerances. For example, a parameter that is substantiallymet may be at least 90% met, at least 95% met, at least 99% met, or even100% met.

FIG. 1 illustrates an electrically driven valve actuator 100. FIG. 1illustrates just one version of an electrically driven valve actuatorand is not intended to limit the applicability of the disclosure to anyelectrically driven or other valve actuator (e.g., a pneumatic actuator,a hydraulic actuator, etc.). Valve actuator 100 includes electric motor104 coupled to worm shaft 103. Handwheel 101 is connected to handwheeladapter 111. Handwheel adapter 111 is connected to drive sleeve 102.Drive sleeve 102 is connected to valve stem nut (not shown). Worm gear110 mates with worm shaft 103. Worm gear 110 is also coupled to a valvestem nut, which is able to drive the valve stem of a valve. In FIG. 1 ,valve actuator 100 is not shown attached to a valve. Operation of eitherelectric motor 104 or handwheel 101 raises or lowers a valve stem. Thevalve stem is able to travel up and down through the center of handwheel101. The valve stem may also rotate and either operate a nut in thevalve which can either open or close the valve or can directly rotate avalve element to an open or close position (e.g., as in a butterfly,vane, or ball valve).

Valve actuator 100 may include any drive train, hardware, devices,electronics, and/or software utilized in operating a valve. Valveactuator 100 may be designed for any type of valve, including forexample, linear, quarter-turn rotary, multi-turn rotary, ball, plug,gate, butterfly, and diaphragm valves. The components of valve actuator100 may be arranged in any fashion. Handwheel 101 may be oriented to theside of valve actuator 100, as is known in the art.

The drive train encompasses any prime mover, any manual operationmechanism, any disengagement or isolation mechanisms, brakingmechanisms, any speed modulation mechanisms, and the mechanisms forattachment to a valve. A drive train may also exclude any of the aboveelements or also include additional elements. For purposes ofillustration only, FIG. 1 shows electric motor 104 as the prime moverand handwheel 101 as the manual operation mechanism. Often, a clutchmechanism will be included so that operation of either electric motor104 or handwheel 101 does not result in operation of the other. By wayof example, a lever 105 and a declutch mechanism 113 can be provided asthe disengagement or isolation mechanisms. Numerous clutch andengagement mechanisms are known in the art. Declutch mechanism 113 maybe designed to engage or disengage any portion of the drive train ofvalve actuator 100.

In FIG. 1 , the locking and braking mechanism is incorporated in wormshaft 103 and worm gear 110. Instead of, or in addition to, worm gear110 and worm shaft 103, other gear types or no gears may be used invalve actuator 100. Gear types for valve actuators are often selectedbased upon the amount of speed reduction, if any, between electric motor104 and valve stem nut. Hereinafter, when referring to the gears of thedrive train of a valve actuator, the example of a worm gear and a wormshaft are primarily utilized. However, it should be understood that thediscussion may be applied to any gear. If a gear is not present in thevalve actuator, then output mechanism of any applicable prime mover mayalso suffice.

In the example of FIG. 1 , the mechanisms for attachment to a valve maybe a valve stem nut and associated supporting structures, as are knownin the art. However, any mechanism for attachment known in the art maybe utilized. The term “valve” as used herein encompasses the mostgeneric uses of the term as used in the art, including the definition ofa device, assembly, or system that at least partially controls the flowof a liquid, gas, and/or solid. Electric motor 104 may be anyelectrically driven prime mover capable of operating a valve actuator.

The valve actuator 100, when running, may move the valve at or near itsrated design speed (e.g., which may be the actuator's full speed) untilthe motor 104 is de-energized. When moving a valve to its closedposition the actuator 100 will move at its rated speed until the valvereaches its closed position (e.g., a seat position), whereby the outputtorque produced by the actuator 100 increases. If the torque levelreaches a predetermined trip level, the motor 104 may be de-energized.Such a torque seating method of closing a valve may secure a valve inthe closed position terminating the process flow. In other embodiments,other elements of the valve system may be monitored to determine whenthe valve reaches the closed position. For example, a control system(e.g., control system 106, discussed below) may monitor the position ofa valve element, the position of a shaft of the valve, one or morecharacteristics of the valve actuator (e.g., power consumption, acurrent level supplied to the motor, a position of the motor, heatoutput of the motor, etc.), one or more characteristics of the valve(e.g., a characteristic of flow or pressure in or through the valve), orcombinations thereof

FIG. 1 also illustrates an exemplary control system 106 for the valveactuator 100. For example, the control system 106 may include a controlmodule 108 for controlling electric motor 104, and depicts electronics115 for receiving inputs from an interface (e.g., control panel 107) andfor sending outputs to indicator 112. In this particular example,indicator 112 is illustrated as a liquid crystal display (LCD). One ormore indicators 112 may be present. A few non-limiting examples ofindicators include light-emitting diode lights (LED) and displays,filament lights, and dials.

The control system 106 may also include one or more sensors fordetermining positions of portion of the valve (e.g., a valve element,which provides a physical barrier to the flow in a closed position andenables flow in an open position). For example, the control system 106may include an encoder 109, which is depicted as a multi-wheel absoluteencoder in FIG. 1 . In other embodiments, the encoder 109 may comprise adifferent type of encoder such as, for example, a single wheel absoluteencoder, an incremental encoder, etc. Other type of position sensors maybe utilized, such as, for example, magnetic sensors, inductive sensors,capacitive sensors, etc.

In some embodiments, the control panel 107 may be part of the controlsystem 106. In other embodiments, the control panel 107 may be formedseparate from and remotely communicate with the control system 106(e.g., where the control system 106 is located remote from the actuator100). In any instance, the control system 106 and/or the control panel107 may provide user instructions and/or automated instructions (e.g.,in the form of executed coded instructions) that may operate the valveactuator and/or other portions of the valve assembly or system.

The present disclosure is not limited to any particular valve actuatorand may be applied to any valve actuator. FIG. 2 illustrates apneumatically driven valve actuator, valve actuator 140, as known in theart. Valve actuator 140 is shown mated to valve 136 and actuator stem122 is coupled to valve element 132 (e.g., shaft 131 and plug 130). Asnoted above, referring to both FIGS. 1 and 2 , the control system 106 ofthe actuator 100, 140 may include position sensing features that maymonitor position of positions of the valve 136, such as, for example,one or more positions of the valve element 132 (e.g., the plug 130and/or its associate shaft 131).

The movement of the actuator stem 122 results in corresponding movementof shaft 131 and plug 130, which governs the operation of valve 136.Valve 136 may be a globe, gate, ball, butterfly, plug, diaphragm, or anyother type of valve operable by an actuator. Actuator stem 122, shaft131, and plug 130 are illustrated for a representative globe valve.However, it should be understood that either component may be modifieddepending upon the type of valve present. Additionally, when the phrase“drive train” is used hereinafter, the phrase encompasses the drivecomponents of valve actuator 140, such as actuator stem 122.

Valve actuator 140 may also include a control system similar to thecontrol system 106 as shown and described above with reference to FIG. 1.

Embodiments of methods, devices, apparatus, and systems of the presentdisclosure may be utilized to operate a valve actuator and to monitorand control such operation. For example, the embodiments of the presentdisclosure may be used to operate a control system of a valve actuatorwhile monitoring at least one parameter or characteristic of a valvesystem in order to periodically alter one or more operations of thevalve actuator.

Embodiments of the present disclosure may include control systems forthe valve actuators such as, for example, an internal control system orexternal (e.g., remote) control system of a valve actuator.

Embodiments of the present disclosure may relate to electric valveactuation, which includes changing (e.g., with an electrically-poweredmotor) a valve position to obtain a desired process flow. As notedabove, other types of valve actuation may be implemented.

The control system may instruct the valve actuator to open a valve froma closed and/or seated position to a mid-travel position within thelimits of travel may initiate a process flow. Conversely, a valveactuator may move a valve to the closed or seated position terminating aprocess flow. Additionally, a valve can be moved from one mid-travelposition to another mid-travel position increasing or decreasing theprocess flow as required.

During a closing or seating event, as the valve begins to make contactwith the valve body (e.g., a seating surface), the resistance to furthermovement of the valve may be restricted due to a hard stop and/or fromother conditions in the valve, such as, fluid flow. This may result in arapid rise in torque that is required from the valve actuator to closethe valve. For example, this torque gradient may be so steep (e.g., overmilliseconds of time) that the final torque applied to the valve by theactuator will exceed the torque trip level of the actuator. In such ascenario, the actuator may not be able to react fast enough to limit thetorque level (e.g., to cease operation), which may result in acceleratedvalve wear that will drive maintenance cycles and/or reduced valveservice life.

Further, depending on the process dynamics, such a torque seating methodcan create a rapid reduction in process flows through the valve, whichmay generate process control transients that may disrupt other processcontrol elements in the flow process loop. Further still, if the torquegradient is severe enough, failure of the valve and associated pipingmay result.

FIG. 3 is a chart illustrating a method of operating a control system(e.g., control system 106) of a valve actuator (e.g., valve actuator100). As shown in FIG. 3 , in an act, the control system instructs thevalve actuator to move the valve from an open position (e.g., a fullyopen position, a partially open position) toward (e.g., to) a closedposition.

In some embodiments, the open position may be unobstructed. For example,the open position may lack a hard stop or back stop that would prohibitfurther movement of the valve element past a certain open position. Inother words, the control system may move the valve element in adirection away from the closed position to an open position where thevalve element is capable of moving past the open position in thedirection away from the closed position. In the case of rotating valveelement, it should be noted that as the valve element moves away formthe closed position in one direction (e.g., along one arcuate path), thevalve element may be moving relatively closer to the closed position inanother direction (e.g., along another arcuate path).

In some embodiments, a closed or seated position may include positioningthe valve element at a hard seat that is substantially immovablerelative to the movable valve element of the valve (e.g., by initiallycontacting the seat and then forcing the valve element into the seatwith the actuator). For example, the valve may comprise a butterflyvalve that contacts a hard stop and then is forced into the hard stop ina closed position where the seats (e.g., metal or polymer seals) definea substantial barrier to fluid flow through the valve. In otherembodiments, a closed or seated position may include positioning thevalve element into a position or seat where further movement of thevalve element is substantially unrestrained. For example, the valve maycomprise a ball valve that is positioned in a select orientation in aclosed position where the seats (e.g., metal or polymer seals) define asubstantial barrier to fluid flow through the valve. However, in such anembodiment, the valve element may be moved beyond the closed or seatedposition.

FIG. 4 shows an example graph indicating profiles of movement of thevalve between an initial position (e.g., an open position, a closedposition, variations therebetween) and a commanded or target positioninto which the valve actuator is going to move the valve element (e.g.,an open position, a closed position, variations therebetween). By theway of example, moving the valve element from an open position to aclosed position is discussed below. However, in other implementations,the valve element may be moved between two open positions, from a closedposition to an open position, etc. As further discussed below, thecommanded position may relate to characteristic of the valve. Forexample, a characteristic of fluid flow, such as, flow rate, pressure,and/or pressure differential may be stipulated and the control systemmay move the valve element until such a condition is substantiallyachieved at a corresponding position. In some embodiments, using knownparameter of the valve, the control system may make an initialcalculation to predict an approximate position in which such acharacteristic may be achieved.

Referring to FIGS. 3 and 4 , the control system instructs the valveactuator to move the valve (e.g., the valve element) from an openposition toward a closed position. The valve actuator may accelerate thevalve element to a run speed (e.g., which may be a partial, full, or amaximum speed of the motor of the actuator). In some embodiments, thecontrol system may calculate and/or monitor the acceleration of thevalve element as it is ramped up to the run speed (e.g., by monitoringthe time taken to reach the run speed from a stationary position).

After maintaining the run speed for a period of time (e.g., where theposition, such as, the angular position, may be monitored by the controlsystem), the control system may begin to decelerate the valve element.As depicted, such an act may commence at a determined decelerationposition. In some embodiments, the determined deceleration position maybe calculated (e.g., based upon speed), directly sensed (e.g., bysensing position of the valve element by an encoder or other positionsensor), combinations thereof, etc.

Once arriving at the deceleration position, the speed of the valveelement may be reduced to the valve seat approach speed (e.g., toperform a soft close of the valve element). As discussed above, a closedor seated position may include positioning the valve element at a hardseat that is substantially immovable relative to the movable valveelement of the valve or positioning the valve element into a position orseat where further movement of the valve element is substantiallyunrestrained.

The actuator may maintain this approach speed until the valve issubstantially closed (e.g. entirely closed). A closed valve may bedetermined as discussed above, for example, by a valve element position(e.g., as measured by an output shaft encoder), by seat torque asmeasured by the actuator, by monitoring one or more characteristics ofthe valve (e.g., a current supplied to the motor, flow or pressurethrough the valve), or combinations thereof.

In some embodiments, the control system may monitor a firstcharacteristic of the valve (e.g., position of the valve element,position of a shaft of the valve or actuator) as the valve element ismoving along a path toward the closed position (e.g., along the pathwhere the valve element is traveling at the run speed and/or a portionof the path at the approach speed). At a location along the path, thecontrol system may switch to monitoring another characteristic of thevalve (e.g., one or more of a torque or a current of the valve actuator)as the valve element approaches and reaches the closed position alongthe path (e.g., along the path where the valve element is traveling atthe approach speed).

In some embodiments, the control system may calculate and/or monitor thedeceleration of the valve element as it is reduced to the approach speedfrom the run speed. For example, the control system may monitor the timetaken to reach the approach speed from the run speed (e.g., the timetaken to travel from the deceleration position to the approachposition).

Over time, the valve closed position may drift from the closed positionthat is initially or previously configured into the actuator (e.g.,through direct input by a user, through sensing a closed position,etc.). In some embodiments, such drift may occur though wear of one ormore components of the valve (e.g., wear experienced by the valveelement, the seating surfaces, etc.) and/or through material buildup onone or more components of the valve (e.g., buildup on the valve element,the seating surfaces, etc.). In some embodiments, as such wearaccumulates over time, the actual closed position may drift movingfurther away from the open position extending the actuator traveldistance to the closed position. In some embodiments, material may buildup on the valve, for example, as precipitants of the process flow,oxidation of valve material interaction with process, etc. In this andother embodiments, the valve close position may be closer to the openposition reducing the valve travel.

Regardless of the direction and/or magnitude of the drift, the controlsystem may monitor deviation from the initial valve closed position,which may indicate change from the originally configured operatingcondition. Such deviation may be calculated at intervals or each timethe valve element is moved to a closed position. The control system maysense (e.g., via a position sensor) the new or deviated position of thevalve element in the closed position and record the new position. Thedrift or deviation may be calculated by comparing (e.g., calculating thedifference between) the initial position and the new or present closedposition.

As depicted in FIG. 4 , once the new closed position is determined, thecontrol system may then adjust the profile utilized in closing and, insome embodiments, opening the valve. For example, as depicted in FIG. 4, a baseline profile (e.g., the centerline in the deviation band) mayaltered to the left of the graph (e.g., when the valve seat has driftedrelatively closer to the open position) or to the right (e.g., when thevalve seat has drifted relatively further away from the open position).

By way of further example, through an adaptive control algorithm, thecontrol system may utilize the newly sensed seated or closed position ofthe valve element (e.g., the measured deviation/drift of the closed orseated position) to dynamically adjust (e.g., to recalculate based onbaseline parameters in the control system) one or more of thedeceleration position and the approach speed position.

As depicted in FIG. 4 , while the control system may dynamically updatedrift of a seated or closed position, the control system maysubstantially maintain (e.g., entirely maintain) the open position. Forexample, the control system may dynamically alter the distance betweenthe open and closed positions while substantially maintaining theposition of the predetermined open position.

In other embodiments, the control system may alter the open positionrelative to the change of the closed position. In yet other embodiments,the control system may dynamically alter the position of the openposition based on one or more values monitored by the control system.For example, the control system may alter one or more of acharacteristic of fluid flow through the valve (e.g., pressure in theflow, flow rate, flow regime, such as laminar, turbulent, or variationstherebetween). In response to such a sensed or monitored value, thecontrol system may actively adjust the open position until an acceptablevalue is obtained (e.g., a value in a set range stored in the controlsystem).

In some embodiments, as the drift exceeds a certain set point (e.g., apredetermined deviation band), a message and/or alarm may be generatedto inform maintenance and operations of the drift, optionally with anindication of which direction the drift is occurring. Such an alarmmessage can also include possible causes of such deviation and suggestedactions.

Use of such an adaptive speed position profile control algorithm may actto mitigate many of the problems noted above in a seating event. In someembodiments, changing the valve seating approach speed characteristic isone method to reduce/eliminate at least some of the unwantedcharacteristics in moving a valve between positions (e.g., as discussedabove). For example, reducing the valve closing speed prior to valveseating may greatly enhance the ability to control the seating event,thereby, yielding a less aggressive torque gradient, reduced peak torqueovershoot, reduced valve wear, and reduction in process flowdisruptions.

In some embodiments, such application of a motor control technology withclosed-loop variable speed and closed-loop torque control (e.g., controlof power or current to the motor) may implement soft seating of thevalve along with adaptive control enabling the control system todynamically monitor and update various positions of the valve, such as,the closed and open positions. In some embodiments, a control system forthe valve actuator may implement motor control technology such as, forexample, a direct current (DC) motor drive or an alternating current(AC) variable frequency drive with field oriented control. The controlsystem may further include one or more sensors for monitoring actuatoroutput shaft position (e.g., an encoder or other position sensor) andone or more sensors for measuring an output and/or input related tocomponents of the actuator, such as, for example, an output shaft torque(e.g., via motor current or torque-force sensing device), powerconsumption (e.g., current) and/or operating temperature of the motor.Implementing an algorithm to command a reduction in approach to seatspeed as the position of the valve approaches the seat position maycreate a smoother controlled transition to the seated position. Once atthe seated position, the algorithm transitions from a closed-loopspeed-position mode to a closed-loop torque control mode, increasing theactuator torque output to the desired final torque level. The motor isthen de-energized and the valve is now securely seated in the closedposition.

In some embodiments, such monitoring of the torque with the controlsystem may indicate if a valve is wearing out or sticking. Further,trending patterns in the torque measurements may enable predictivemaintenance.

As discussed above, in some embodiments, the control system may beutilized in a somewhat similar manner to that shown in FIGS. 3 and 4 ,to move a valve element between one or more positions where there is nophysical hard-stop to the movement (e.g., rotational movement) of thevalve element. Such a configuring also lacks a hard-seated position andassociated torque ramp-up and torque trip-out at the end of travel asdescribed above. Such a valve configuration (e.g., a modulating controlvalve) may have physical locations and geometries where flow may beshutoff, full open, and/or throttled in between open and shutoff orclosed positioned defining differing operating ranges.

In the instance of a modulating control valve, such a valve may be usedto accurately adjust a process flow or pressure. The fluid flow can bemeasured directly by a flow sensor or by measuring the differentialpressure across the valve.

FIG. 5 is chart illustrating a method of operating a control system of avalve actuator, for example, where the positions are unobstructed (e.g.,lack a hard stop). As noted above, such position may includecombinations of multiple open positions of the valve element and aclosed or seat position lacking a hard stop.

Referring to FIGS. 4 and 5 , when moving a valve to a commanded ortarget position lacking an associated hard stop, the actuator will moveat its rated speed until the valve reaches the commanded position, wherethe motor is de-energized and the motion stops. However, the actuatorhas likely overshot the commanded position triggering a correction inthe form of a movement in the opposite direction. As this correction isgenerally a relatively small movement, the duration that the motor isenergized is also small, perhaps even just a quick pulse. It is furtherlikely the actuator will again overshoot and initiate a correction inthe original direction. Such hunting/oscillation will continue until theerror between the commanded position and actual position falls withinthe control loop's deadband parameter (e.g., a range where the positionerror is small enough that no further action required). If the deadbandparameter is not set correctly (or another gain parameter), theoscillation could continue indefinitely resulting in reduced actuatorlife and creating process disturbances in the flow loop. In someinstances, the actuator may over heat (e.g., thermally trip)de-activating the actuator for a period of time for cool down where theprocess is temporarily not actively controlled.

Implementing a closed-loop process algorithm as discussed above toregulate a reduction in approach speed as the valve approaches thecommanded position, flow rate, and/or desired pressure may generate asmooth controlled transition from movement to a stop. Overshoot andhunting/oscillation about the desired process parameter may be reducedor eliminated enabling for faster process start-up, less wear on theactuator and valve, and greater process stability.

Referring to FIGS. 4 and 5 , the drift may be characterized as processerror where such error is a function of the difference between a setprocess variable (e.g., position, flow, and/or pressure) and a processset point for that process variable. The characteristics of thisoperational profile may be parameterized by the operator, or,dynamically calculated (e.g., learned) with the implementation of anauto-tuning algorithm. The later offers a dynamic update to controloperation and/or characteristics of the valve ensuring optimizedperformance through the operating envelope. The dynamic update may alsoadjust for changing environmental conditions, flow materials, and/orequipment wear, all of which may impact the actuator operation andprocess stability.

The valve actuator performance may be benchmarked utilizing one or moreinitial valve positions to establish the desired processcharacteristics. Over time, wear/buildup on the valve may cause theseone or more positions to change and the control system may update thesepositions to generate substantially the same process characteristic. Asthe one or more positions drift from the benchmarked position(s), analarm may be generated once the drift exceeds an operator defineddeviation band. Such an alarm may inform operators and maintenanceresources of the changing system performance which may be an indicationof eroding system health and potential system failure.

In some embodiments, the control system may monitor one or morecharacteristics of valve (e.g., a torque profile) as compared to abaseline scenario. As discussed above, the valve actuator may be fittedwith a torque limiting apparatus. This apparatus may cause the motor tobe de-energized if the torque generated by the actuator exceeds thetorque set with the limiting technology. Replacing or supplementing thetorque limiting technology with a dynamic direct torque measurementtechnology may enable the actuator to monitor the torque generatedthroughout the valve movement. The torque profile may be benchmarked andthe torque profile of subsequent valve movements can be monitored andcompared to the torque profile baseline.

As the actuator and valve wear and/or as the environmental and/oroperating conditions change, deviations between the actual measuredtorque profile and the benchmark torque profile will increase. As thesedeviations begin to exceed deviation limits, an action (e.g., one ormore alarms may be generated to alert operators and maintenanceresources of the changing operating dynamic of the system indicatingpossible deterioration of the health of the system. In some embodiments,analysis of the evolving torque profile may be utilized to suggestproblem areas in the system to investigate as the root cause of thedeviation.

In some embodiments, the control system may monitor one or more thermalvalues in the valve system. For example, as the actuator moves thevalve, the prime mover of the system is the electric motor in theactuator, which will generate heat energy during operation. The rate ofthermal rise may be determined, in part, by one or more of (1) thenumber of moves per unit time, (2) the load on the motor (e.g., thetorque required to move the valve at the commanded speed), (3) ambienttemperature, and (4) construction, thermal rating, and heat dissipationdesign of the electric motor.

For example, running the motor many times with a high load at themaximum speed in a very warm environment will result a high thermal rise(e.g., increase in temperature). Such a scenario may limit how much theactuator may be used to move the valve as components of the actuatorhave an operational temperature rating in their design specifications.Driving the equipment beyond these thermal ratings may seriouslydeteriorate this equipment, or worse, cause them to fail. Generally, ifthe actuator exceeds the rated motor operating temperature, the actuatoris stopped to dissipate the heat until the temperature returns to theoperating range.

In some embodiments, as actuator installations may include missioncritical applications, stopping an actuator to cool may not beacceptable.

In some embodiments, the control system may monitor the currenttemperature and/or the rate at which the motor temperature is rising.The control system may predict, based on the actual motor temperatureand/or rate of change, when the actual motor temperature will exceed thetemperature specification. In such a scenario, the adaptive controlalgorithm may slow the speed of the motor, thereby, reducing the thermalrate and enabling the actuator to continue operating withinspecification operation. While this action may not entirely prevent theactual motor temperature from eventually exceeding specification, suchthrottling of the motor will extend the operating window for theactuator.

As the rate of thermal rise is decreased, the throttling may be reduceduntil the motor temperature begins to rise again or full operationalcapability is restored.

While certain embodiments have been described and shown in theaccompanying drawings, such embodiments are merely illustrative and notrestrictive of the scope of the disclosure, and this disclosure is notlimited to the specific constructions and arrangements shown anddescribed, since various other additions and modifications to, anddeletions from, the described embodiments will be apparent to one ofordinary skill in the art. Thus, the scope of the disclosure is onlylimited by the literal language, and legal equivalents, of the claimsthat follow.

What is claimed is:
 1. A valve system comprising: a valve actuator forcontrolling a position of a valve element in a valve in order to controlflow through at least a portion of the valve; and a control system forcontrolling the valve actuator, the control system configured to:instruct the valve actuator to move the valve element toward anunobstructed first position in the valve to enable fluid flow throughthe at least a portion of the valve; instruct the valve actuator to movethe valve element from the unobstructed first position to a secondclosed position in the valve to reduce the fluid flow through the atleast a portion of the valve, wherein the valve element is at leastpartially seated to reduce the fluid flow in the valve in the secondclosed position; monitor at least one characteristic of the valve systemduring movement of the valve element to the second closed positioncomprising a hard stop; determine a drift of a sensed location of thesecond closed position based on the monitored at least onecharacteristic of the valve system by calculating a difference between apreviously recorded closed position and the second closed position; andduring each movement of the valve element, maintain a predeterminedlocation of the unobstructed first position while actively adjusting thelocation of the second closed position comprising the hard stop eachtime the drift in the sensed location of the second closed position isdetected.
 2. The valve system of claim 1, wherein the control system isfurther configured to: reduce a rate of speed of the valve element asthe valve element travels to the second closed position at a selectedpoint; and update the selected point for the reducing of the speed ofthe valve element based on the determined drift of the second closedposition.
 3. The valve system of claim 1, wherein the control system isfurther configured to at least one of: determine that the second closedposition of the valve element has drifted to a location relativelycloser to the first position; or determine that the second closedposition of the valve element has drifted to a location relativelyfurther away from the first position.
 4. The valve system of claim 1,wherein the control system is further configured to update adeacceleration point based on the determined drift.
 5. The valve systemof claim 1, wherein the control system is further configured to, at apredetermined location along a path of the valve element, switch tomonitoring another characteristic of the valve system that is distinctfrom the at least one characteristic as the valve element approaches andreaches the second closed position along the path.
 6. The valve systemof claim 1, wherein the at least one characteristic comprises at leastone of torque of the valve actuator, current of the valve actuator, rateof flow through the valve, flow type through the valve, position of thevalve element, or a pressure in the valve.
 7. The valve system of claim1, wherein the control system is further configured to monitor at leastanother characteristic of the valve system during movement of the valveelement back to the first position.
 8. The valve system of claim 7,wherein the at least another characteristic comprises at least one offlow through the valve, flow type through the valve, position of thevalve element, or a pressure in the valve.
 9. The valve system of claim1, wherein the unobstructed first position comprises a position of thevalve element that lacks a hard stop, and wherein the second closedposition comprises a hard stop.
 10. The valve system of claim 1, whereinthe control system is further configured to: update a location of thesecond closed position based on the detected drift; and update alocation of a change in speed of the valve element based on the detecteddrift.
 11. The valve system of claim 1, wherein the control system isfurther configured to generate an alarm or alert when the drift isoutside of a selected range of drift values.
 12. The valve system ofclaim 1, wherein the second closed position comprises a closed seatedposition, and wherein the control system is configured to move the valveelement into contact with a seat of the valve system and then to forcethe valve element into the seat until a selected value of torque in thevalve actuator is reached.
 13. A valve system comprising: a valveactuator for controlling fluid flow through at least a portion of avalve with a valve element; and a control system for controlling thevalve actuator, the control system configured to: instruct the valveactuator to move the valve element to a target position from an initialposition in the valve to reduce or increase fluid flow through the atleast a portion of the valve, the initial position being an unobstructedposition; monitor at least one characteristic of the valve system duringmovement of the valve element to the target position; detect a locationof the target position based on the monitored at least onecharacteristic of the valve system; and during each movement of thevalve element, the control system being further configured to at leastone of: move the valve element into contact with a seat of the valvesystem in the target position and then to force the valve element intothe seat until a selected value of torque in the valve actuator isreached; or maintain a predetermined location of the initial positionwhile actively adjusting the location of the target position based onthe monitored at least one characteristic of the valve system each timethe valve element is moved to the target position.
 14. The valve systemof claim 13, wherein the control system is configured to monitor atorque of the valve actuator as the valve element is positioned at thetarget position.
 15. A method of operating a control system of a valveactuator, the method comprising: moving a valve element with the valveactuator to a closed position to substantially inhibit fluid flowthrough at least a portion of a valve; determining a drift of the closedposition based on the monitored at least one characteristic of the valvesystem; and at least one of: moving the valve element into contact witha seat of the valve system in the closed position and then forcing thevalve element into the seat until a selected value of torque in thevalve actuator is reached; or maintaining a predetermined location ofthe open position lacking a hard stop in the valve to enable fluid flowthrough the at least a portion of the valve while actively adjusting thelocation of the closed position based on a monitored at least onecharacteristic of the valve system each time the valve element is movedbetween the open position and the closed position.
 16. The method ofclaim 15, further comprising monitoring at least another characteristicof the valve system during movement of the valve element to the openposition.
 17. The method of claim 15, further comprising: monitoringposition of the valve element as the valve element is moving along apath toward the closed position; and at a location along the path,switching to monitoring at least one of a torque or a current of thevalve actuator as the valve element approaches and reaches the closedposition along the path.
 18. The method of claim 15, further comprising:reducing a rate of speed of the valve element as the valve elementtravels to the closed position at a selected point; and update theselected point for the reducing of the speed of the valve element basedon the determined drift of the closed position.
 19. The method of claim15, further comprising locating the control system at a location remotefrom the valve.